Amino acid lecture2

Malignant hyperphenylalaninaemias type IV and V BH4 (tetrahydrobiopterin) is lacking due to the defective dihydrobiopterin biosynthesis from guanylate, or an ineffective reduction of BH2 to BH4.
Hypertyrosinaemias
occur in several forms. They may be caused by a deficit of enzymes which catalyze either the transamination of tyrosine, or oxidation of p-hydroxyphenylpyruvate and hydrolysis of fumarylacetoacetate. A low-tyrosine diet may be very useful.
Plasma levels of tyrosine are elevated, and large amounts of tyrosine, p-hydroxyphenylpyruvate, –lactate, and –acetate are excreted into the urine.
Alkaptonuria
is an inborn deficit of homogentisate oxidase characterized by the excretion of homogentisate in the urine. Except for the darkening of the urine on the air, there are no clinical manifestations in youth until the second or third decade, when deposits of pigments in the connective tissue begins to appear (ochronosis – bluish colouring of the scleras, the ear and nasal cartilages, etc.) which are the cause of deforming arthritis.